Oxidation process



NOV- 1955 w. G. TOLAND, JR 2,722,549

OXIDATION PROCESS Filed July 50, 1953 2 Sheets-SheetZ NOQHVO TOOXIDATION FIG.2

Nolln'l s DNIZIGIXO INVENTOR W/LL/AM G. TOLAND JR. BY 2 /v-n/ ATT EYSFEED United States Patent Ofiice I 2,722,549 Patented Nov. 1, 1955 12,722,549 OXIDATION PROCESS William G. Toland, JL, San Rafael, Califi,assignor to California Research Corporation, San Francisco, Calif., acorporation of Delaware Application July 30, 1953, Serial No. 371,209 3Claims.. (Cl. 260-524) This invention relates to a process for oxidizingorganic compounds.

This invention is a continuation-in-part of my copending applicationSerial No. 202,389,, filed December 22, 1950.

Pursuant to the invention, an organic compound, a water-soluble sulfate,a water-soluble sulfide and water are introduced into a reaction zoneand the mixture is there heated to an elevated temperature above 200 F.to effect oxidation of the organic compound.

All types of organic compounds appear to undergo oxidation when treatedin this manner- Organic compounds containing at least onecarbon-to-hydrogen bond andpreferably at least one carbon-to-carbonbond, such as aliphatic hydrocarbons, aromatic hydrocarbons, amines,aldehydes, ketones, esters, organic acids and heterocyclic organiccompounds are readily oxidized by the process of the invention. Theprocess is especially effective for oxidizing hydrocarbons and organiccompounds consisting of carbon, hydrogen and oxygen atoms.

Any inorganic sulfate may be employed in the oxidation process. However,it is preferred to employ watersoluble sulfates whose cations combinewith sulfide ion to form water-soluble sulfides but water-insolublesulfates of metals forming insoluble sulfides may be used elfectivelyprovided an excess of water-soluble sulfide is employed. Ammoniumsulfate, alkali metal sulfates, the water-soluble alkaline earth metalsulfates, the alkali and alkaline earth hydrogen sulfates and sulfuricacid are especially suitable sulfates. Of the several preferredsulfates, ammonium sulfate has been found to be substantially moreeffective. than the metallic sulfates and by its use optimum conversionsand yields are obtained under any fixed set of reaction conditions. Itis believed that the superior character of ammonium sulfate is relatedto the fact that the pH of the water solution of this sulfate and thesulfide or other sulfur compound containing sulfur at a valence belowplus 6 is usually below 9 at room temperature. It has been noted that incomparable solutions where other sulfates are employed, pH values above9 may be obtained and that the reaction proceeds less satisfactorily inthese cases. In, addition to this aspect ammonia liberated fromamomniurn sulfate during the reaction appears to solubilize hydrocarbonfeeds and thus increase the intimacy of contact of the reactants. 1

Any water-soluble sulfide may be, employed in the oxidation. Hydrogensulfide, ammonium sulfide or ammonium polysulfide are preferred,especially when ammonium sulfate is employed as the oxidizing agent.Other sulfides such as the alkali metal sulfides and alkaline earthmetal sulfides are fully operative. While water-soluble inorganicsulfides are preferred, organic polysulfides and water-insolublesulfides which dissolve to an appreciablev extent in hot aqueousammonium sulfate, for example, ferrous sulfide, aluminum sulfide andcadmium sulfide and the like, can be used. As noted hereinafter, theeffective oxidizing agent in the process of the invention is sulfateion. It is most effective especially from the standpoint of rate whenused in combination with a relatively large amount of water and a smallamount of a water-soluble sulfide. The sulfide appears to function as aninitiating reducing agent in the reaction.

The oxidation reaction is conducted at temperatures above 200 F. Whilethere appears to be no upper temperature limit for the reaction, it ispreferred to conduct the reaction at temperatures above 200 F. and belowthe critical temperature of water. More desirably, temperatures above400 F. and below about 700 F. are employed, especially temperatures inthe range from 550 F. to 675 F In the preferred embodiment of theinvention, the oxidation reaction is conducted at an elevated pressuresufficient to maintain a part of the Water introduced into the reactionzone in liquid phase, desirably at pressures in the range from 200 to5000 p. s. i. g.

The vigor and completeness of the oxidation reaction increases withtemperature and the completeness of the oxidation of the organiccompound tends to increase with reaction time. Organic compounds differappreciably in the ease with which they may be oxidized pursuant to theinvention, some being rapidly and completely oxidized at temperaturesbelow 500 F while others require temperatures in the range from 600 to700 P. if oxidation is to be accomplished in a reasonably short period.

The oxidation may be conducted either batchwise or in a continuousprocess. When batch operation is employed, the organic compound, thesulfate, the sulfide and water are introduced into a bomb or anautoclave which is then sealed and heated to reaction temperature withshaking to facilitate contact of the reactants. The size of the bomb isso. related to the quantity of the reactants introduced that anautogenous pressure in the range 1000 to 4000 p. s. i. g. is built upinsuring the presence of liquid water during the reaction. After thereactants have been held at reaction temperature for a time sufiicientto effect thedesired degree of oxidation of theorganic compound, the,bomb is cooled, depressured, and the reaction product removed. Thereaction may also be run continuously, in which case a tubular reactionzone is employed. The reactants are passed through an elongated tube atreaction temperature and under an elevated pressure and the reactionproducts are continuously withdrawn from the reaction zone and purified.

Figure l of the appended drawings illustrates a preferred modificationof the process of the invention. In starting the reaction, ahydrocarbon, for example, a xylene, ammonium sulfate, ammonium sulfide,and water are introduced into reaction zone 1. The reactants are heatedin reaction zone 1 to a temperature in the range from reaction zone 1,either intermittently or continuously, and charged to cooling anddepressuring zone 2. In zone 2 separation of liquid and vapor phase iseffected and a portion of the vapor phase comprising hydrogen sulfide,ammonia and water vapor is returned to reaction zone 1 for use inoxidation of further quantities of xylene. The reaction mixture in zone2 is depressured and the reaction product gases other than those whichhave been recycled are passed into scrubbing zone 3 where the gas isscrubbed-with, sulfuric acid to remove ammonia and to form ammoniumsulfate. The liquid product is removed from zone 2 and passed intoclarification zone 4 where it is mixed with a small quantity ofadsorbent charcoal and filtered to remove any color bodies which mayhave been formed. The filtrate from zone 4 is passed into hydrolysiszone 5 where it is treated with a strong acid, preferablysulfuric acid,and heated to hydrolyze acid amides and to liberate. free phthalic acidsfrom ammonium phthalates contained in the filtrate. The acidified liquidproduct is Figure 2 of the appended drawings is a diagrammaticillustration of apparatus and process flow which has been foundcompletely adequate for the practice of the invention on a pilot plantscale. When the oxidation of metaxylene to isophthalic acid isundertaken using the arrangement of apparatus shown in Figure 2,meta-xylene is Withdrawn from storage tank 11 through line 12 at therate of 56 pounds per hour and pumped by pump 13 through line 14,booster pump 15 and heat exchanger 16 into heating coil 17 in theinterior of furnace 18. An oxidizing solution is withdrawn from storagetank 19 and forced by pump 20 through line 21 into line 14, where itmixes with the xylene and passes into heating coil 17. The oxidizingagent consists of ammonium sulfate, ammonium polysulfide and water.These materials are introduced into line 14 at the rate of 123 pounds ofammonium sulfate per hour, 314 pounds of water per hour, and 14.8 poundsof ammonium polysulfide per hour. The ammonium polysulfide is composedof 8.8 pounds of ammonium sulfide and 6 pounds of elemental sulfur. Inheating coil 17 the mixture of xylene and oxidizing agent is heated toabout 630 F. The hot mixture passes from heating coil 17 to a soakingcoil 22 where the temperature of the mixture is maintained at about 630F. and then passes out of furnace 18 through line 23, heat exchanger 16where it is in indirect heat exchange with fresh feed and the oxidizingagent, through line 24 into stripper 25. The residence time of themixture of xylene and oxidizing agent in the furnace is about 35 to 40minutes. When a xylene feed having a substantial p-xylene content isbeing oxidized it is desirable to insert a high temperature surge drumin line 24. The product is held in this drum at 300-500 F. for 10 to 30minutes during which a moderate amount of vapor is bled from the drum.This treatment reduces the content of sparingly soluble diamides in theoxidation product. In stripping zone 25 the reaction product mixture isstripped with steam to remove carbon dioxide, hydrogen sulfide, ammoniaand some water overhead through line 26. The overhead product passesthrough condenser 27 where a liquid condensate consisting principally ofaqueous ammonium sulfide is formed. This condensate is withdrawn throughline 28 and passed into a first sulfur dissolving vessel 29. 8.9 poundsof ammonium sulfide and 61 pounds of water pass through line 28 intosulfur dissolving vessel 29 each hour. The uncondensed portion of theoverhead passes from condenser 27 through line 30 into scrubber 31. 4pounds of water, 13.5 pounds of carbon dioxide, 16 pounds of ammonia and31 pounds of hydrogen sulfide pass through line 30 into scrubber 31 eachhour. Sulfuric acid is introduced into scrubber 31 through line 32. Thehourly fiow through line 32 is 46 pounds of sulfuric acid, 216 pounds ofwater and 61 pounds of ammonium sulfate. In the usual practice of theinvention, the meta-xylene is oxidized to isophthalic acid which appearsin the primary reaction product in the form of ammonium salts andamides. This salt-amide product is hydrolyzed by contacting it with amolar excess of sulfuric acid to liberate isophthalic acid. Thehydrolysis product is filtered to recover isophthalic acid as the filtercake and an aqueous filtrate containing ammonium sulfate and sulfuricacid. This filtrate is introduced into scrubber 31 through line 32 andcontains suflicient sulfuric acid to scrub ammonia from the gas streamentering scrubber 31 through line 30. The sulfuric acid and gases areintimately mixed in scrubber 31 where the ammonia contained in the gasesis converted to ammonium sulfate. Unabsorbed gases are withdrawn fromscrubber 31 through line 33. 31 pounds of hydrogen sulfide, 13.5 poundsof carbon dioxide and about 0.8 pound of water are withdrawn fromscrubber 31 through line 33 each hour. The hydrogen sulfide withdrawn isoxidized to sulfuric acid which is then used to hydrolyze the salt-amideproduct and returned to the process by introducing it into scrubber 31through line 32.

Aqueous ammonium sulfate is withdrawn from scrubber 31 through line 37.119 pounds of ammonium sulfate and 219 pounds of water are withdrawnfrom scrubber 31 through line 37 each hour. The effiuent from scrubber31 is forced through line 39 and filter 40 into storage tank 19 by pump38. Ammonia is introduced into line 39 through line 41 at the rate ofone pound per hour to neutralize residual sulfuric acid in the efliuentfrom scrubber 31.

The stripped oxidation reaction product accumulates in the lower portionof stripper 25 where a lower liquid sulfur phase and an upper aqueousphase containing phthalic acid values separate. The aqueous phase iswithdrawn from stripper 25 through line 35 and passed into surge tank36. Liquid sulfur is withdrawn from the bottom of stripper 25 throughsteam-traced line 34 and passed into sulfur-dissolving vessel 29 whereit is intimately contacted with aqueous ammonium sulfide. The liquid mixis withdrawn from sulfur dissolver 29 through line 42 and passed into asecond sulfur dissolving vessel 43 where the liquid is further agitatedto complete the dissolving of the elemental sulfur in ammonium sulfide.Ammonium polysulfide is withdrawn from dissolving vessel 43 through line44 and passed through filter 45 and line 46 into storage tank 19. 8.8pounds of ammonium sulfide, 6.1 pounds of sulfur and 61 pounds of waterpass through line 46 into storage tank 19 each hour, the ammoniumsulfide and sulfur being in the form of ammonium polysulfide. Theaqueous phase of the reaction product passing into surge tank 36 throughline 35 contains the phthalic acid values produced during the oxidationstep. The aqueous mixture flowing into surge tank 36 each hour contains0.15 pound of ammonium sulfate, 326 pounds of water, 27 pounds ofammonium isophthalate, 43 pounds of isophthalic acid monoamide, 8 poundsof isophthalic acid diamide, 4 pounds of ammonium orthophthalate, 1.4pounds of ammonium benzoate and .8 pound of ammonium toluate.

The ammonium orthophthalate and ammonium benzoate are produced byoxidation of ortho-xylene and ethyl benzene contained in the xylenefeed. It will be noted that the sulfate content of the oxidationreaction product is very low, essentially all of the sulfate having beenreduced as it oxidized the xylene feed.

The aqueous phase recovered from stripper 25 is passed from surge tank36 through line 47 and pumped by pump 48 through filter 49 into vessel50. Activated charcoal is added to vessel 50 through line 51 at the rateofl 1.3 pounds per hour. The activated carbon is intimately mixed withthe aqueous liquid in vessel 50 and then withdrawn from vessel 50through line 52 and pumped by pump 53 through line 54 and filter 55where the carbon and color bodies contained in the aqueous liquid areremoved into storage tank 56.

The clear aqueous liquid is withdrawn from storage tank 56 through line57 and conducted to hydrolysis and purification of the phthalic acid.

The following examples illustrate in detail the manner in which alkylaromatic hydrocarbons may be oxidized to produce aromatic carboxylicacids by the process of the invention.

EXAMPLE 1 The apparatus employed in this experiment was a stainlesssteel bomb having a capacity of 4.5 liters. The bomb was fitted with apressure gauge, a thermowell, a bursting disk, a bleed line and valve,and a shaker. g. of paraxylene (98.8% para-), 305 g. of ammoniumsulfate, 4.65 moles of ammonium sulfide in water solution having avolume of 700 cc., and 1150 cc. of water were introduced into the bomb.The bomb was sealed and heated to 600 F. and held at that temperaturefor one hour. The bomb was then cooled to room temperature, opened, andthe reaction product was removed. The reaction product was stripped withsteam, and filtered to remove approximately 1 g. of sulfur. The filtratewas acidified with hydrogen chloride to precipitate the insolubleorganic acids, and filtered. The filter cake was washed and dried. 69 g.of unreacted para-xylene were recovered during the steam stripping step.The filter cake weighed 102 g., had a neutral equivalent of 131, and asaponification equivalent of 113. The solid product consisted ofterephthalic acid, toluic acid, and amides of both acids. The acidproducts contained 47% by weight of phthalic acids and their derivativesand 53% of toluic acids and their derivatives.

6'. in weight is due almost entirely to absorption of hydrogen sulfide.

The liquid product was steam-stripped and filtered to remove sulfur.This: filtrate was acidified with hydrochloric acid to precipitatephthalic acids. The acidified 5 EXAMPLE 2 filtrate was filtered and thephthallc acid filter cake was The procedure followed in Example 1 wasrepeated. z g 3 9 z 2 welghttofl thlsgltfr Z The amounts of thereactants employed were the same. d ca 6 4" g 8 f The only difference inthe procedure was that the bomb t1 qg ca fi o th yle 0 was heated to 600F. and held at that temperature for a 10 g z cl was we g per can eperiod of 6 hours. rg EXAMPLE 4 The filter cake recovered in thisexperiment Weighed 240.6 g., had a neutral equivalent of 109 and asaponifica- The data from additional runs in which the specific tionequivalent of 81.8,. The filter cake consisted essencomposition of theoxidizing agent is varied are summartially of terephthalic amides andacid. ized in the following Table I.

Table l d l T P Cqnver- Yield, Re 665021 oxidizing 62.. a H1021 in;

Percent emen 660-1 Toluene (1 mole) NH4HSO4 (1.5 moles) 700 600 1.01,800 Benz oic Acid 8 Low. E28 (4.64 moles) V 721/16 Para-xylene (1.5{(NH4 2SO4(2.31T101S) H} 1,850 600 1.0 2,800 Terephthalic Acid 89 128moles). NHa (8.9 moles) NE 88.9 and To- 6 3 168 NH luio Acid.

. m0 3 721 20 .410 iaa moles His} 2, 000 600 1.0 2, 550 TerephthalicAcid 7.0 NazSOi (4.6 moles) NE 118 and; To-

luic Acid.

The filtrate obtained in this experiment was evaporated v 5. and theresidue was extracted with chloroform. The A number f il scale runs didi i i chloroform was evaporated and 10g. of white solid matures fmetaand para.xylencs Th xylem f d terial were recovered. Th s materialconsisted of toluic mined varying amounts of orthoq yljene ethylbenzene, and benzoic acids. and paratfins. Under the conditions of thereaction, the The yield of phthalic acid was 96.2% of theory. paraffinsare Oxidized principally. to carbon dioxide and EXAMPLE 3 the quantityof oxidizing agent employed, was, adjusted:

to be suflicient to, accomplish substantially complete conapparatusemployed m Example 1 I used m thls version of the xylenes in addition toessentially. complete, experiment. The charge, to the bomb consisted of1 mole oxidation of the Paraffin and ethyl bqnzpne impuriticsdk I ofpara'xylene 218 of ammomum sulfate 800 of 40 The mixture of oxidizingagent and xylene in these runs water and 200 g. of hydrogen sulfid Thebomb was was passed through a preheat section made up of 60 ft. heatejdto a temperature of 600 held at temperaof inch steel pipe and thenthrough a reactor section ture m the range from 583 to for a period f11/2 consisting of 420 n. of /4 inch steel pipe. The data of hours.During this period the pressure in the bomb varied representative runsare summarized in the' following between 2400 and 2800 p. s. i. g. Thebomb was cooled Table II.

Table II oxidizing Mixture Xylene Molar Feed Ratio R N Ems v1 A un OnIsomer. pprox stream (M10260. 111s (NHQzSx i-g Ratio, gig; f f f gggfgBlend cc./n1in.

4.6 v v 8 v 4 1:1.59: .16:27' 3 v v 2 v. v 1:1.61: 01:26 04 v 4 s 35121.83: .18: 3,0 21-25 v v v 1:l.81:.731:21

Reaction Conditions Feed Quantities Product Work-up a nd Yields XyleneMole Yields Est. 0x1- Percent Run N0 Temp. Pres- Residizing Com AcidvCarboxyl gg Sure $31106 Space version N o A .s.i ime 1011, I mi 9 p(mm) Lbs. Lbs. Phthahes 'lolmcs Groups to room temperature and opened.When the bomb was EXAMPLE 6 opened, the gases escaping from the bombwere passed through a caustic scrubber. The scrubber showed a gain inweight of 200 g. when the passage of the gases from the bomb through ithad been completed. This increase Table III.

A further series of runs was made .in a. larger pilot unit:corresponding to Figure 2 of the appended drawings. The. data of theseruns were summarized, in. the following Table III Oxidizing Mixtureifigg Molar Feed Ratio 1131.111 Egurs 0. un Percent Molethyl Ammo- Ammo-Free Free o-wm-fiyn-xy- Paraf- Hydro- (NHmSOi (NHOZS (NHmSx ten bcnniummum Sul- Water Sulfur lane lane lene zene fins carbon Sulfate Sulfidefur Feed Quantities Product Work-up, Yields and Analyses HydrocarbonMole Percent Yield Temp. Pressure Hydro- Run N9 F. p. s. i g $5 3 5Oxid. carbon Product water, soln., Space ponver- Acid lbs. lbs.Velocity, N o-PAc M'P Toluics Benzoic vllvJhn cent PAc EXAMPLE 7 Anumber of representative organic compounds was oxidized by heating themto temperatures in the range Temper- Material ature Reaction Productfrom 400 to 700 F. with a water-soluble sulfate, a wateri e solublesulfide and water pursuant to the invention. The organic compound,temperature of reaction, and products Nitrot-oluenc 600 Carbonaceous.obtained are summarized in the following Table IV. The g-gflgggg gg ggigg gig fi ggg gf acid products listed are recovered by springing theacid Ethyl fuereu teu I 000 Acetic acid. from the salts and amides inthe crude reaction product 288 pmpifx'lic acid With a strong mineralacid. 40 Oyclohexaue 550 Succinic acid and lower aliphatic acids. TableIV Cyclohexene 450 Phenol quinonc, hydro- (1111110110. n-butanol 600Acetic, propionic, butyric Temper acids. Material alsulgo, ReactionProduct EXAMPLE 3 'loluic acids 545 Phthalic acids. Ce mio acid 535-590Carbon dioxide. 135 g. of meta-xylene, 188 g. of alummum sulfate, 1375'figli'fffff: 228 Acegfcid Succinic acid g. of Water and 41 g. ofhydrogen sulfide were charged to butyricacid,CO:. a 4.5 liter autoclave.The autoclave was sealed and ggff ff x Z28 acid the mixture was heatedto 600 F. and then shaken for cyclggeiflnonfififiinu 7 53 Phentfi ailnd00 one hour. The autoclave was cooled and the gases were a-me y nap aene5 5-5 a-nap t oic aci a pmtiambutyl toluene H 5504500 p mmary butylbemoic bled through a caustic scrubber where carbon dlOAldC was acid.recovered. The liquid products contained 50.4 g. of ung g fig x ggggffif g gg reacted xylene. The water layer of the liquid productPseudocumene 600 ortbgphthallligfi ilsophtgalic 5.3 had a. pH 2 and astrong odor of hydrogen sulfide. The mcwnene 600 gg f g g water layerwas filtered and a wet cake weighing 20 9 g. gonzyl 21001101...." 288gaentzoic Z1l10tig.1 d was obtained. The filter cake was digested w1thsodium ureue SO- OTBP I a 1C 201 S. 2,3-dimethyl butane. 600 00.,iso-butyric acid hydroxide and water and filtered. The filtrate wasacidi u'hexane 600 (302, lowcrhaliphatig acirzlfj fied to pH 5 and thenfiltered hot. The filtrate was then octane r 600 tgff glf am 5 0acidified to pH 1 with concentrated hydrochloric acid toTrimethvlacetiwcidrecipitate organic acids. A light gray precipitate was2 2 4-tr1methyl pcntane 600 p l h obtained WhlCl'l has a neutralequivalent of 121.4 and 600 {Trimethylpropionicacidconsisted principallyof benzoic acid. Diamyl sulfide 600 Mixed1 aciils, plgdzglzlg nant y yaeric aci 63 EXAMPLE 9 t-butyl p-xylene 630 t-butyl terephthalic acid.

'lrimethylaceticacld. 106 g. of a mixture of metaand para-xylenes con-Dusobmflene 500 Trimethylpropionicacid. 1 h d lfid Heminellitene 00Phthafic Rh talnlng 5 y 34 gof Y rogen Sn 6, 212 Ie th0 1gl. 0 1 t Co g.of l1th1um sulfate monohydrate and 960 cc. of water l'lIIlB y amine A 10 y mcrcap an, 2. Dodecem (propylene p01ymer) Aliphatic acids (NE 2348)were charged to a 2.5 l1.er autoclave. The autoclave was t uty Xylene ku tr g n g g l0 sealed and heated to 620 F. for one hour. The autoigifliig fi f clave was cooled and gases were bled through a caustic g WL 5 scrubber where carbon dioxide was recovered. The liquid g figgg Iproduct contained 89 g. of unreacted xylene. The Water Sulfonw mi 620usulfobenzow phase of the liquid product was treated substantially as 1n,,f h 600 136mm mm Example 1. An organic acid solid phase which had aneutral equivalent of 162.5 was precipitated. The acid was principallytoluic acid.

EXAMPLE 10 Example 9 was repeated, substituting 251 g. of ferroussulfate for the lithium sulfate of Example 9. The liquid productcontained 46 g. of unreacted xylene. An Organic acid phase having aneutral equivalent of 128.2 was recovered from the aqueous phase of theliquid product. The acid was principally a mixture of benzoic and toluicacids.

As indicated above, the process of the invention is conducted atelevated temperatures. A temperature above 400 F. is desirable ifreasonable reaction rates are to be obtained with most organiccompounds. Preferably, higher temperatures in the range from 500 to 700F. are employed to obtain high conversions in reasonably short periodsof time. Most desirably, the reaction is conducted at temperatures inthe range from about 575 to 650 F. Where xylene feed is to be oxidized,it appears that the optimum temperature for the reaction is in the rangefrom about 620 to 650 F.

The reaction is conducted under a superatmospheric pressure sufiicientto maintain a substantial proportion of the water in liquid phase. Wherebatch operation is employed, the autogenous pressure built up in asealed reaction vessel is a satisfactory pressure, it being understoodthat the quantity of reactants charged be so related to the volume ofthe reaction vessel that all of the water cannot exist in vapor phase.When the process is conducted continuously by passing the reactionmixture through a tubular reaction zone, the pressure in the tubularreactor is controlled by valves and held at a level in the range from1000 to 5000 p. s. i. g. or, more desirably, in the range from 2000 to3500 p. s. i. g.

The net reaction when xylenes are oxidized is shown by the followingequation:

CONHs) (C ONHz)2 The mixture of ammonium phthalate, ammonium phthalatemonoamide and phthalic diamide aggregates 1 mole in the above equation.

As indicated by the above equation, 1.5 moles of ammonium sulfate arerequired to oxidize 1 mole of xylene to a phthalic acid product, (i. e.,0.75 mole of sulfate oxidizes one methyl group to a carboxyl group). Amolar excess of ammonium sulfate is desirably employed and ordinarilyfrom about 1.55 moles to 1.75 moles of ammonium sulfate are charged tothe reaction for each mole of xylene fed. Xylene feeds may commonlycontain 5 to 10% of paraffinic hydrocarbons and, where parafiins arepresent, larger amounts of ammonium sulfate will be required to achievecomplete conversion of the xylene, since the parafiin oxidation consumesa relatively larger amount of oxidizing agent.

While the above equation does not show water as a material participatingin the reaction, the presence of water in considerable amount isnecessary for good conversions and yields. For good operation it isdesirable to charge at least 25 moles of water per mole of organiccompound to the reaction zone. 30 to moles of water per mole ofhydrocarbon facilitate good conversions and yields. Even larger amountsof water may be employed, the only adverse effect being that a largerproportion of the available reaction space is occupied by the water sothat the throughput of feed per unit volume of reaction space is lower.

The sulfide component of the reaction mixture serves to increase therate of reaction. The effective oxidizing agent of course is the sulfateion, but its effectiveness, especially from the standpoint of rate, ismarkedly increased by the sulfide. The amount of sulfide charged to thereaction zone is desirably in the range from 0.05 to 0.3 mole per moleof organic compound, and preferably in the range from 0.2 to 0.25 moleper mole of organic feed. Optimum proportions of reactants when a xyleneis being oxidized are 1.6 to 1.7 moles of ammonium sulfate per mole ofxylene, 30 to 40 moles of water per mole of xylene, and 0.2 to 0.3 moleof sulfide per mole of xylene. When the sulfide employed is am moniumpolysulfide, about .25 mole of ammonium polysulfide containing about .38gram atoms of sulfur per mole of xylene appears to be optimum.

I claim:

1. A process for producing phthalic acids which comprises contactingxylenes with ammonium sulfate, ammonium polysulfide and water in areaction zone at a temperature in the range 550 to about 650 F. under asuperatmospheric pressure suificient to mantain a part of the water inliquid phase, the mole ratio of sulfate to xylene being in the range ofabout 1.55:1 to 1.75:1 and the mole ratio of polysulfide toxylene beingin the range of about 0.05:1 to 0.321.

2. The method as defined in claim 1, wherein the xylene is meta-xylene.

3. The method as defined in claim 1, wherein the xylene is para-xylene.

No references cited.

1. A PROCES FOR PRODUCING PHTHALIC ACIDS WHICH COMPRISES CONTACTINGXYLENES WITH AMMONIUM SULFATE, AMMONIUM POLYSULFIDE AND WATER IN AREACTION ZONE AT A TEMPERATURE IN THE RANGE 550 TO ABOUT 650*F. UNDER ASUPERATMOSPHERIC PRESSURE SUFFICIENT TO MANTAIN A PART OF THE WATER INLIQUID PHASE, THE MOLE RATIO OF SULFATE TO XYLENE BEING IN THE RANGE OFABOUT 1.55:1 TO 1.75:1 AND THE MOLE RATIO OF POLYSULFIDE TO XYLENE BEINGIN THE RANGE OF ABOUT 0.05:1 TO 0.3:1.